1. Technical Field
The present invention relates to a photopolymerizable photosensitive resin composition and to a method for forming a hydrogel from the composition.
2. Background Art
Poly((meth)acrylic acid) and an alkali-neutralized product thereof are highly miscible with hydrophilic physiologically active substances such as drug ingredients and enzymes. Thus, for the purpose of retaining and immobilizing hydrophilic substances, such polymers are employed in wastewater treatment and as a base material for a diagnostic drug, a cataplasm, etc. In most cases, such a base material is hardened under hydrous conditions through cross-linking so as to retain and immobilize a substance of interest. The thus-hardened product is generally called “hydrogel.” Water plays important roles in hydrogel, including dissolving a substance in a film-form substrate, controlling rate of releasing a substance to the outside, and controlling rate of mass diffusion from the outside.
Conventionally, hydrogel of poly((meth)acrylic acid) or an alkali-neutralized product thereof is formed through hardening by heat. When a substance having poor thermal stability or a volatile substance is immobilized in gel, the polymer must be hardened at low temperature. Thus, completion of gel formation and immobilization requires a very long period of time (e.g., several days), which is problematic (Japanese Patent Application Laid-Open (kokai) No. 5-320612).
In recent years, a non-thermal method, employing a photocurable resin, for immobilizing a thermally instable physiologically active substance such as an enzyme or bacterial cells has become known as an advantageous method in the art, as discussed in Japanese Patent Publication (kokoku) No. 8-23545, and Japanese Patent Application Laid-Open (kokai) Nos. 2-240555 and 2-308805.
Among photosensitive resins disclosed in the above documents, so-called PVA-SbQ resin has drawbacks. Specifically, since PVA-SbQ resin has a cationic moiety in the molecule, only limited compounds may be dissolvable or miscible in immobilization of a physiologically active substance, an enzyme, or bacterial cells. In addition, in the presence of a large amount of water, photosensitivity of PVA-SbQ resin decreases considerably. Thus, when a compound that cannot be subjected to a drying step is immobilized under hydrous conditions, the formed gel has poor strength, due to insufficient hardenability.
Another photopolymerizable composition, which is a composition containing a cellulose-based polymer, has poor photosensitivity. When such a composition is used, an additional polymerizable monomer is required to be incorporated into the composition so as to attain sufficient hardenability. However, complete polymerization of the polymerizable monomer through photocuring reaction is virtually impossible, and the remaining unreacted monomer problematically inhibits enzymatic activity or causes skin irritation. Thus, the cellulose-based polymer composition is difficult to employ for immobilizing enzymes or producing a cataplasm.
Conventionally, there is a known technique for introducing a polymerizable cross-linking moiety into poly((meth)acrylic acid) by use of a (meth)acrylate ester having an epoxy group. This is described in Japanese Patent Application Laid-Open (kokai) No. 49-98878. However, the document does not disclose a photocurable and water-containing composition, and the disclosed approach polymer cannot be employed for the formation of a hydrogel, which is an object attained by the present invention.
Similarly, there techniques have previously been reported for introducing a cross-linking group into a poly((meth)acrylic acid) copolymer by use of a (meth)acrylate ester having an epoxy group. These are described in Japanese Patent Application Laid-Open (kokai) Nos. 10-3167 and 4-337087. Although the above copolymers are photocurable, the copolymers are provided for use in photoresist and have a pH-dependent water-solubility; i.e., have poor solubility in water under weak acidic to neutral conditions. Thus, the copolymers exhibit insufficient physical properties, including miscibility with other compounds and water content of gel during the formation of a hydrogel, which is an object attained by the present invention.
As described above, poly((meth)acrylic acid) is a key compound for formation of hydrogel for use in a cataplasm, a diagnostic drug, or wastewater treatment, and photocuring is an effective technique for forming a hydrogel for the above uses. However, a useful technique has previously not been developed employing poly((meth)acrylic acid) and photocuring in combination.